Recently, electronic equipments have become thinner, lighter and smaller. Accordingly, electronic parts to be mounted in the electronic equipments have also become smaller. Silicone adhesive tapes have been widely used as an adhesive tape in processing because of their high heat resistance and as an adhesive tape in transfer because of their good peelability.
However, silicone adhesives are electrically highly insulating and, therefore, may cause peeling electrification and, at worst, may cause a dielectric breakdown of the electronic part when a thin and small electronic part is peeled. In order to prevent the peeling electrification, it is needed to develop an antistatic silicone adhesive.
For example, Patent Literatures 1 and 2 describe antistatic adhesive tapes whose tape substrates are antistatic. Such adhesive tapes have problems that tape substrates to be used are limited, and peeling electrification is not prevented in a case where the adhesive is electrically insulating. Patent Literatures 3, 4 and 5 describe antistatic adhesive tapes having an antistatic layer between an adhesive layer and a tape substrate. The use of an adhesive tape worsens productivity due to steps of the production of the adhesive tape. Further, peeling electrification is not prevented in a case where the adhesive is electrically insulating, as described for the aforesaid antistatic adhesive tape.
Patent Literatures 6, 7, 8 and 9 describe antistatic adhesive tapes whose adhesives are antistatic. Patent Literature 6 describes that the adhesive comprises carbon black. Patent Literature 7 describes that the adhesive comprises a polyol. Patent Literatures 8 and 9 describe that the adhesive comprises electrically conductive microparticles dispersed therein.
A polyether polyol is less compatible with a silicone adhesive. Therefore, the adhesive comprising the polyol may be cloudy and cause separation of the polyol with time. The compound needs to be added in a large amount and, therefore, the adhesive comprising the compound may not have a desired adhesion strength. Further, in a case where this adhesive is used to form an adhesive tape, a strength of bond between the adhesive and a tape substrate is lower, so that the adhesive may remain on a tape-stuck body when the adhesive tape is peeled from the tape-stuck body. The adhesive comprising carbon black has such disadvantages that washing of an apparatus for producing an adhesive tape is a troublesome work due to carbon black; the adhesive tape has an opaque, black appearance and an unstable surface resistivity; and carbon remains on a tape-stuck body such as an electronic element after the adhesive tape is peeled from the tape-stuck body. Further, the adhesive comprising electrically conductive microparticles is opaque, and may not attain a desired performance due to separation of the electrically conductive microparticles caused by a difference in specific gravities between the adhesive composition and the electrically conductive microparticles.
Patent Literature 10 describes a silicone adhesive composition comprising an ion conductive antistatic agent which is a lithium salt, and that a silicone adhesive tape comprising the adhesive composition has an excellent antistatic property and maintains the antistatic property even after exposed to a high temperature for a long time. This Literature also describes that the antistatic property is improved by adding the ion conductive antistatic agent in such a manner that the agent is dissolved in an organic solvent having an oxyalkylene group. Patent Literature 10 refers to the following compounds as the organic solvent having an oxyalkylene group:R3—(C═O)—O—(R4—O)m—R5 wherein R3 is an alkyl group having 1 to 12 carbon atoms, R4 may be identical to or different from each other and are each a polymethylene group having 2 to 8 carbon atoms, R5 is a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and m is an integer of 2 to 50, andR6—(O—R7)n—O—(C═O)—R8—(C═O)—O—(R7—O)p—R6 wherein R6 may be identical to or different from each other and are each a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, R7 and R8 may be identical to or different from each other and are each an ethylene group or a polymethylene group having 3 to 12 carbon atoms, and n and p may be identical to or different from each other and are each an integer of 2 to 50.